The present invention relates to a drug delivery system, particularly a system utilizing pumps of the negative pressure type for continuous delivery of drugs.
It is known in the prior art to administer fluids to a patient in a number of ways. For example, a solution such as saline, glucose or an electrolyte in a glass or flexible container is fed intravenously by gravity to a patient's venous access site via a length of flexible plastic tubing such as polyvinylchloride tubing. Flow from the container to the patient may be regulated by means of a roller clamp.
However, such gravity-feed type systems are of limited application. This is particularly so where continuous or controlled application of drugs is required. For example, in the treatment of pain related conditions, it is known in the art to use a number of electro-mechanical pumping systems to deliver drugs to the patient. A number of positive pressure pumps, e.g. of the plunger type, are known in the field. An example thereof is the pump sold under the trade designation "Lifecare PCT+2 Infusion System" available from Abbott Laboratories. However, such positive feed systems suffer from a number of difficulties. For example, with positive pressure systems, after the pump stops, flow contents of the system may continue to be expelled or sucked back because of the positive pressure already created in the syringe, thus making control less accurate. Further, with systems such as the Abbott Lifecare system, specially designed drug vials must be utilized.
It is also known in the prior art to utilize negative pressure pump systems for the delivery of drugs. The drug is drawn from a vial rather than being expelled. For example, a peristaltic pumping action is particularly well suited for this purpose. An advantage is provided because peristaltic pumping action may be applied externally of the tubing carrying the intravenous or like fluid. Thus, sterile conditions of the fluid are maintained within the tubing while imparting propulsion to the fluid. Also, the peristaltic pumping action may be applied at any point along the tubing.
In a common type of peristaltic pump known in the prior art, a driving motor is connected to an array of cams angularly spaced from each other. The cams in turn drive cam followers connected to corresponding pressure fingers, which act on a flexible tubing that is carrying the intravenous fluid. The pump elements cooperate to impart a linear wave motion on the pressure fingers that moves the fluid along in a pulsatile flow.
Whereas such negative pressure systems provide significant advantages over the positive pressure systems known in the art, difficulties still remain with the peristaltic pump type arrangements. For example, containers utilized with the peristaltic systems are flexible bags, which are initially empty and which must be filled with fluid by the operator. Such containers are inconvenient to fill, difficult to use, and increase the danger of inadvertent spillage or contamination.